Of all the legendary Hollywood’s love stories and affairs, perhaps the most complicated is Spencer Tracy and Katharine Hepburn’s. Though carefully concealed from the public, on screen the iconic duo shared their time on total nine different films, starting with the 1942 classic “Woman of the Year” and coming to an end with the ever indelible “Guess Who’s Coming to Dinner” in 1967.

Tracy and Hepburn first met on the set of “Woman of the Year,” when he was 41 and she was 34. Their initial impressions were similar to a screwball comedy, with Hepburn’s first words to Tracy were “I fear I may be too tall for you, Mr. Tracy,” and his being wary of her, even suspecting that she was a lesbian. At the beginning, the pair addressed each other as “Miss Hepburn” and “Mr. Tracy,” but within a week after they changed to first-name terms. Gene Kelly, a co-star on the film, once recalled, “At lunch time they’d just meet and sit on a bench on the lot. They’d hold hands and talk – and everybody left them alone in their little private world.”

Their relationship, however, was kept in secret, with Tracy determined to conceal the affair from his wife, even as M.G.M was to prevent a controversy; needless to say, it still remained an open secret in Hollywood at the time. They were extremely careful to avoid being seen together in public and maintained separate residences, though Tracy did settle into a cottage near Hepburn’s house in Beverly Hills. Throughout the pair’s 26-year-long romance, Tracy remained married and Hepburn never fought for marriage. According to Joan Fontaine, he could “get a divorce whenever I want to, but my wife and Kate like things just as they are.”

Intimate as it seemed from the outside, theirs was not a healthy relationship, since Tracy’s was a troubled soul. He was known to be an alcoholic and frequently depressed. Hepburn described him as “tortured;” Louise, his wife, called him “the most volatile person I’ve ever seen – up in the clouds one minute and down in the depths the next.” Behind closed door, a heavily drunk Tracy bellowed at his devoted mistress until he passed out, and even once smacked his hand across her face. Hepburn, however, devoted herself to make his life more peaceful. From people who saw them together, her usual strong-willed and self-involved demeanor changed into an almost submission whenever she was around Tracy, who was also heavily dependent on her. She mothered, obeyed and always put his demands first. “I wanted him to be happy, safe, comfortable. I liked to wait on him, listen to him, feed him, work for him. I tried not to disturb him. I was happy to do this.”

In the sixties, when Tracy’s health significantly deteriorated, Hepburn took a five-year hiatus in her career to take care of him. She moved into his house for this period, stayed by his side when he passed away on June 10, 1967. Mindful of his family, Hepburn did not attend Tracy’s funeral, though she did call his wife to see whether a peace between them could be reached, to which Louise responded, “I thought you were a rumor.”

It was not until Louise’s death, in 1983, that Hepburn began to break her public silence on her feelings for Tracy. At this time she had befriended his daughter, Susie. In response to the question of why she stayed with Tracy for so long when their relationship could never become official, she replied, “I honestly don’t know. I can only say that I could never have left him.” Briefly after that Hepburn added that she did not know exactly the nature of Tracy’s feelings toward her, but that they “just passed twenty-seven years together in what was to me absolute bliss.”

“I loved Spencer Tracy,” Hepburn wrote in her 1991 autobiography, “I would have done anything for him.” Below are 36 photos and stills capturing their intimate moments on screen.